I've done an extensive amount of reading on this topic lately. I have a 2K XJ Sport, and I am attempting to mount factory fogs using a factory dash switch - installing everything as close to factory standards as possible. The Sport (at least mine) was not fully wired for fogs. It is my understanding that most Classics were.
I can tell you that the first next step should probably be checking to see that your PDC is wired for the appropriate relays. If it is, then your second next step should be to pull the dash panel and check to see if you have the fog light rocker switch wiring (almost all models do, but if they did not come equipped with factory fogs, the wires terminate at the fuse panel). But, if you have the relays AND the switch wiring you might be lucky enough to have a simple plug and play situation, here.
If so, I envy you.